1. Field of the Invention
This invention relates to a low-section pneumatic radial tire having an aspect ratio of not more than 0.85.
2. Related Art Statement
In general, various problems in the low-section pneumatic radial tire having an aspect ratio of not more than 0.85 are produced by ground contact deformation during running under loading after inflation at a given internal pressure. Two large troubles among them, are particularly uneven wear based on the large size growth at a point separating inward from shoulder end by a distance corresponding to about 1/4 of tread width such as unsymmetrical wear, shoulder wear or the like; and belt end separation based on shearing force between plies at belt end. In order to overcomes the troubles as mentioned above, there has hitherto been proposed a low-section radial tire as disclosed in Japanese Patent laid open No. 60-22,504. In this tire, a pair of reinforcing bands each containing cords embedded at a cord angle of not more than 5.degree. are arranged outward from the belt in the radial direction and at both sides with respect to the center of the belt in such a manner that when a distance ranging from the belt center to an end of the belt is L, a distance ranging from the belt center to an inner end of the reinforcing band is within a range of 0.2L to 0.4L and a distance ranging from the belt center to an outer end of the reinforcing band is within a range of 0.7L to 0.8L.
In the conventional low-section radial tire, the region causing a large size growth is surely restrained to uniformize the growth amount over the entire width of the tread, so that the former trouble, i.e. the unevenness can surely be prevented. However, the ground contact pressure at the central region of the tread in its widthwise direction is merely reduced by the uniformization of the growth amount to lessen the heat build-up of the tread. Hence, that the shearing force between the plies at the belt end during the running under loading can not be reduced and consequently the belt end separation can not effectively be prevented.
On the other hand, U.S. Pat. No. 4,271,890 discloses that a limiting block is arranged between the belt ply and the carcass and is formed of two plies containing cords arranged at a cord angle smaller than that of the belt ply with respect to the circumferential direction, the cords of which plies being crossed with each other. In this case, the shearing force at the belt end is reduced, but it is apt to cause separation failure at the end of the limiting block through the shearing force.